ION-BEAM AMORPHIZATION OF MUSCOVITE MICA

The microstructure of a muscovite mica exposed to a rare gas ion beam has been studied by transmission electron microscopy. The investigatio n of damage without implantation was carried out using argon and heliu m ions of sufficient energy to traverse the 100-150 nm mica specimens. For 340 keV Ar++ irradiation, amorphization of mica occurred at a flu ence as low as 3.5 X 10(14) ions . cm(-2), which corresponds to 0.29 d pa. Muscovite can be amorphized using 80 keV helium ions, but this req uires a much higher fluence and damage production of 4.6 X 10(16) ions . cm(-2) and 0.60 dpa, respectively, Since helium irradiation results principally in ionization energy loss, it indicates that amorphizatio n of muscovite results mainly from nuclear interactions. Complete amor phization of muscovite mica is found to take place for all ions at app roximately the same amount of nuclear energy transfer to energetic pri mary knock-on atoms, assuming a recoil energy greater than 500 eV. Thi s suggests that amorphization occurs directly in dense displacement ca scades. A significant amount of helium, 100 ppm, can be implanted into muscovite mica without destroying the crystal structure.